R/defineStrata.r

In BradHubley/SpatialHub: Survey Design and Spatial Analysis of Fisheries Data

#' @title defineStrata
#' @description defines strata boundaries using the sqrt(f(y)) rule (Cochran 1977)
#' @param char = vector of values of the variable used to define strata
#' @param nstrata = number of strata desired
#' @param min.str = minimum value of stratifing variable considered
#' @param max.str = maximum value of stratifing variable considered
#' @param place = decimal places used to define strata boundaries
#' @importFrom stats var
#' @author Brad Hubley
#' @export

defineStrata<-function(char,nstrata=4,min.str=0,max.str,place=0){


	bin<-round(char,place)
	if(missing(max.str))max.str<-max(bin)

	bins<-sort(unique(bin[bin>0]))
	vars<-c()
	avg<-c()
	N<-c()
	srN<-c()


 	for(i in 1:length(bins)){

		avg[i]<-mean(char[bin==bins[i]])
		vars[i]<-var(char[bin==bins[i]])
		N[i]<-length(char[bin==bins[i]])
		srN[1]<-sqrt(N[1])
		if(i>1) srN[i]<-sqrt(N[i])+srN[i-1]
 	}

  	ideal.div<-max(srN)/nstrata*(1:nstrata)
  	ind<-c()
  	for(i in 1:length(ideal.div)){
		ind[i] <- which(srN==srN[abs(srN-ideal.div[i])==min(abs(srN-ideal.div[i]))])
	}

	str<-c(min.str,bins[ind])
	str[length(str)]<-max.str

	str

}